This invention relates in general to vehicle transmissions and in particular to an improved system for synchronizing the speeds of various rotating members to enable smooth gear shifts in a vehicle transmission.
In most vehicles, a transmission is provided in the drive train between the engine and the driven wheels. As is well known, the transmission includes a housing containing an input shaft, an output shaft, and a plurality of meshing gears which are selectively connected between the input shaft and the output shaft. The meshing gears contained within the transmission housing are of is varying size so as to provide a plurality of speed reduction gear ratios between the input shaft and the output shaft. By appropriate selection of these meshing gears, a desired speed reduction gear ratio can be obtained between the input shaft and the output shaft. As a result, acceleration and deceleration of the vehicle can be accomplished in a smooth and efficient manner.
Typically, this gear ratio selection is accomplished by moving one or more control members provided within the transmission. Movement of the control member causes certain ones of the meshing gears, referred to as "ratio gears", to be connected between the input shaft and the output shaft so as to provide the desired gear ratio between the input shaft and the output shaft. In a manual transmission, movement of the control member is accomplished by manual exertion of the vehicle driver, such as through a shift lever. In an automatic transmission, movement of the control member is accomplished by a pneumatic, hydraulic or electrical actuator in response to predetermined operating conditions.
In typical vehicle transmissions, the mechanism to engage various gears is the axial movement of splined, rotatable members into engagement with each other. A control member, such as a splined clutch collar, is moved axially from a neutral position to a position in which the clutch collar splines engage the splines of a rotatable ratio gear. The ratio gear may be linked indirectly to the transmission input shaft. The splines of the clutch collar also engage the splines of a rotatable drive gear, such as a hub, which is linked to or directly mounted on a drive shaft, such as a mainshaft. Thus, the clutch collar is rotatably mounted and is moveable axially to simultaneously engage the splines of the ratio gear and the hub, thereby connecting the mainshaft to a specific driven gear.
In order to accomplish the engagement of the various gears in a smooth manner, the rotating members, such as the clutch collar and the ratio gear which are to be interconnected, must be rotating at approximately the same rate. Otherwise, the splines of the one rotating member will not be able to intermesh with the splines of the other without crashing. Various ways are known for synchronizing the speeds of various rotating members. A commonly used synchronizing apparatus employs a series of frustoconically shaped rotatable members which nest with generally parallel contact surfaces. At least one of the frustoconical surfaces is connected directly or indirectly to one of the rotating splined members, and another of the frustoconical surfaces is connected to the other of the rotating splined members. An initial movement of the splined members toward each other causes the frustoconical surfaces, rotating at different speeds, to be pressed together. The frictional force between the frustoconical surfaces causes an equalization of speeds, thereby enabling the complete engagement of the rotating splined members.
One of the problems with synchronization devices in the past is that they require extensive tooling and are expensive to make. Also, they require a significant amount of labor for manufacture and assembly. Consumers' demands for more smoothly operating and rapidly shifting transmissions means that even more powerful synchronization devices are required. In a synchronization system using frustoconical surfaces, one method for increasing the power is by using more of the frustoconical surfaces, thereby providing more area for frictional forces to take effect. However, adding additional frustoconical surfaces increases the cost of the synchronization device. Another method for increasing the power of synchronization devices is to increase the diameter or distance from the axial centerline at which the torque generated by the frictional force between adjacent frustoconical forces is applied. Moving the force radially outwardly increases the moment arm and thereby increases the torque applied by the frictional forces. Unfortunately, increasing the distance from the axial centerline also increases the size and weight of the synchronization apparatus, which is an undesirable result. Also, the volume within the transmission is not unlimited, and increasing the diameter of the synchronization device may not be feasible.
There is a need for an improved synchronization apparatus which provides a higher power density or synchronization capacity within a given volume. The synchronization apparatus should be compact, and should be capable of being assembled with a minimum of labor. Further, the synchronization apparatus should have a low cost in terms of materials, and should have low machining costs.